The Collaborative International Dictionary of English v.0.48:

Vesiculation \Ve*sic`u*la"tion\, n. (Geol.)
   The state of containing vesicles, or the process by which
   vesicles are formed.
   [1913 Webster]

WordNet (r) 3.0 (2006):

vesiculation
    n 1: the formation of vesicles in or beneath the skin [syn:
         vesiculation, vesication, blistering]